Recently, digital broadcasting for broadcasting digital contents has been started. Digital contents hardly suffer degradation due to use. Therefore, in order to protect copyrights of the digital contents, each of the digital contents has CCI (Copy Control Information) attached thereto showing whether copying of the digital content is permitted and the number of permitted copies.
However, when a hard disk recorder (hereinafter “HD recorder”) stores, in an HDD (Hard Disk Drive), a content having CCI attached thereto showing that copying of the content is not permitted, even if the HD recorder protects a copyright of the content based on the CCI, a malicious use might be performed. For example, when the HD recorder is powered off, a malicious user removes the HDD and connects the HDD to a personal computer and the like to copy the content stored in the HDD. As one example of conventional arts for preventing such a malicious copying, the following art is known. In advance, a content stored in an HDD is assigned to a one-way function to calculate illegitimacy detection information, and the calculated illegitimacy detection information is stored in the HDD. When the HD recorder is powered on, a content stored in the HDD is assigned to the one-way function to generate verification information. The generated verification information and the stored illegitimacy detection information are compared with each other to detect a malicious use of the content.
Here, although the HDD is convenient, a failure occurrence rate thereof increases depending on a usage frequency since the HDD reads and writes information by performing a rotational operation or a seek operation. If the HDD fails, the content completely disappears since there exists no copy of the content. In order to prevent such a data disappearance due to the HDD failure, it is effective to back up the content to other recording medium or recoding device.
After a content recorded in the HD recorder is backed up to the recording device, if the content needs to be deleted because of an insufficient recording capacity of the HDD relating to the HD recorder, the backup that is a copy of the content needs to be deleted from the recording device for protecting a copyright of the content while deleting the content from the HD recorder. This is for avoiding that the backup remains for use despite the content has been deleted in terms of copyright protection.